The ARC is pretty neutral and the sound cannot be varied due to its use of 6H30 triodes -- they are only made by Sovtek.
The BAT, like the ARC, uses 6H30's, so you are stuck with its sound (which is somewhat "dark").
You can tinker with the sound of 6H30-based preamps by fooling around with power cords, power supplies, isolation components and other mods, but that is a world of chaos I try not to enter.
The Sonic Frontiers is very neutral, but its sound can be tailored somewhat through tube rolling.
As for other fine balanced tube preamps, the ARC Reference II Mk. I is very close to the best and you can roll tubes (the Ref II Mk. II uses 6H30's). The ARC LS-5 Mk. III is very good as well, and much cheaper.
Another option is the balanced (and it is truly differential balanced) solid-state Rowland Coherence II, which I own. It is quieter than any tube amp (and virtually any other solid-state amp) due to its being battery powered, and most importantly for someone who wants a tube preamp, it layers space better than tube preamps (you don't want a tube preamp because it is euphonic, but rather, because it expands the soundstage out from the speakers compared to typical solid-state preamps). It neither sounds solid-state nor tubey, but does have the tube preamp traits of a bit of warmth to the midrange and very slightly subdued highs. It can be had used for about $6,000-$6,500.
Unless you are stuck trying to resolve dryness or other problems elsewhere in your system, I think that the preamp is a bad place to add a real coloration to the sound. As the nerve center through which all your music passes, a preamp should be as quiet, as transparent, as resolving and as neutral as possible, or otherwise, you will be putting coloration on top of coloration when you go to add other components (and may end up having to throw the whole soup out).
The BAT, like the ARC, uses 6H30's, so you are stuck with its sound (which is somewhat "dark").
You can tinker with the sound of 6H30-based preamps by fooling around with power cords, power supplies, isolation components and other mods, but that is a world of chaos I try not to enter.
The Sonic Frontiers is very neutral, but its sound can be tailored somewhat through tube rolling.
As for other fine balanced tube preamps, the ARC Reference II Mk. I is very close to the best and you can roll tubes (the Ref II Mk. II uses 6H30's). The ARC LS-5 Mk. III is very good as well, and much cheaper.
Another option is the balanced (and it is truly differential balanced) solid-state Rowland Coherence II, which I own. It is quieter than any tube amp (and virtually any other solid-state amp) due to its being battery powered, and most importantly for someone who wants a tube preamp, it layers space better than tube preamps (you don't want a tube preamp because it is euphonic, but rather, because it expands the soundstage out from the speakers compared to typical solid-state preamps). It neither sounds solid-state nor tubey, but does have the tube preamp traits of a bit of warmth to the midrange and very slightly subdued highs. It can be had used for about $6,000-$6,500.
Unless you are stuck trying to resolve dryness or other problems elsewhere in your system, I think that the preamp is a bad place to add a real coloration to the sound. As the nerve center through which all your music passes, a preamp should be as quiet, as transparent, as resolving and as neutral as possible, or otherwise, you will be putting coloration on top of coloration when you go to add other components (and may end up having to throw the whole soup out).